Nenju
are frequently given as gifts - for example - to celebrate a birth,
marriage, a coming-of-age, etc. They are also given as keepsakes
and a source of protection to loved ones.
Nenju
are objects to be treated with respect and taken care of.
They should not be left lying around carelessly, and should be
cleaned and kept in good repair. Nenju that are beyond repair
should be disposed of properly - normally they would be taken
to a Shinto Shrine, where, along with old good-luck charms,
they will be respectfully ritualistically disposed of by the priests.
...
..
Number of beads:
The formal nenju has 108 koshu 'children'/main
beads, plus either one or two larger boshu 'parent' beads.
[The
108 koshu represent the 108 bonnou (earthly desires,
worldly & or evil passions) which the follower of the Dharma
seeks to overcome.]
There are also 'informal' nenju. These are commonly 1/4-size,
having 27 koshu and one boshu parent-bead. However
there are also informal nenju with 18 koshu (1/6th-size),
36 koshu (1/3rd) 54 koshu (1/2).
A
huge 1,080 koshu is sometimes, though rarely, used by priests.
Styles
of nenju:
Different Buddhist schools have slightly different styles of formal
nenju. For example:

Nichiren shu
The formal nenju of Nichiren Buddhism has 108 koshu
'children'/main beads, two larger boshu 'parent' beads
and 4 shitendama 'segment' or ' marker' beads which are
slightly smaller than the 108 koshu beads). The 2 boshu
are placed at opposite ends of the string of koshu beads.
One boshu has 2 strings of additional beads hanging from
it, the other boshu has 3 strings of additional beads.
(the
Nichiren shu only use formal nenju - informal nenju
are not seen as acceptable)
The Nichiren nenju is held in a figure-8 and one end with
a parent bead placed over one middle finger - the other boshu
bead end over the other middle finger, so that the tassle-strings
rest on the backs of the hands and the koshu beads hang
between the palms, which are placed together in gassho.
Shingon
shu
The nenju used by the Shingon shu is similar to
that of the Nichiren school, except that it only has 2 -strings
on each boshu parent bead.
The
nenju also incorporates 4 marker beads. These are positioned
after the 7th bead and 21st bead on either side of one of the
parent beads.
In
prayer, they are held in the same manner as the
Nichiren beads.
Tendai
shu
Tendai nenju have slightly flattened koshu beads
(hiratama) compared to the round koshu used by other
schools.
The nenju is a single strand of 108 koshu, with
4 marker beads, and a single boshu with two strings of
additional beads.
In prayer, the nenju is held between the index and middle
fingers of each hand so that when the hands are placed together
in gassho, part of the strand of flattened koshu
hangs between the palms, and the other end, with the boshu
bead and two strings of additional beads, drapes across the back
of the hand / middle, ring, and little fingers.
Alternatively,
the beads can be placed in a double loop over the fingers
of both hands - letting them rest between the fingers and the
thumb, while bring the hands into gassho.
Jodo
shu
Jodo shu (Pure Land school) has four different
kinds of juzu. One, for example, known as a hyakumanben
is a huge 'communal' juzu used by the whole congregation
who, sitting in a circle, all hold the juzu which is rotated
in a clockwise direction, with each person passing the beads from
their right hand to their left.
A
second juzu, known as the nikka (or: rokumanben
guri nikka) - designed for counting 60,000 recitations of
the nembutsu - is shown here. This juzu consists
of two loops - one loop with forty beads and a parent bead (called
an oyadama); and one loop with twenty-seven beads interspaced
with small beads and one oyadama.
This second loop has a floating metal ring to which two tassles
are attached - one with ten flat beads; and one with six small
round beads.
The juzu is held in the left hand with the twenty-seven
bead loop held between the index and middle fingers and the other
loop between index finger and thumb.
This juzu is either carried hung on the left wrist or held
in the left hand. When the hands are held in gassho (prayer
position) this juzu is draped over the thumbs and allowed
to hang between the wrists.
Jodo Shin shu
This
27 bead nenju of the Jodo shin shu has 2 marker
beads and the parent or 'Buddha bead' has a special tassle-string.
The
tassle-string consists of a large loop and two 'end' pieces. The
loop is seen to represent the cycle of birth & dying; and
the end strings represent the 'cutting' or severing of the cycle
of birth & dying.
In prayer, the beads can be placed over the fingers of the left
hand (or both hands) - letting them rest between the fingers and
the thumb, while bring the hands into gassho.

The formal nenju used by Jodo shin shu has 108 main
beads
and two oyadama parent beads.
Each
parent bead has two large tassles hanging from it. There
are also additional beads on the tassle-strings of one of the
parent beads.
In
prayer, the doubled loop of beads can be placed over the fingers
of both hands - letting them rest between the fingers and the
thumb, while bring the hands into gassho.
Zen shu 
Soto & Rinzai Zen shu use a nenju with a single
loop of koshu and one boshu, from which hangs a
double-tassle. It also has 4 'segment' or 'marker' beads which
are slightly smaller than the 108 koshu beads, and one
slightly larger marker bead. There is also a loose metal ring
on the main loop of beads [this is not present in the Rinzai
shu nenju]
In prayer, the nenju is placed in a double loop on the
left hand.
When not chanting/praying/meditating, the nenju is held in the
left hand.
Photo credits:
Yasuda
Nenju Ten